Imaging apparatus

ABSTRACT

With the imaging apparatus of this invention, an image is divided equally into four areas, and a setting is made for reading of carriers before irradiation to be carried out separately according to images of the divided areas. By dividing the reading of carriers before irradiation in this way, when compared with the reading of carriers for an entire area of an image (i.e. a frame) in the prior art, each storage and reading time can be shortened to one of the number of divisions. A time serving as a starting point of an irradiation wait time occurs before the reading of carriers before irradiation. Consequently, even if the time serving as the starting point of the irradiation wait time varies, the variation takes place only during each storage and reading set short. Thus, the variation of the irradiation wait time is made less than in the prior art, thereby improving response.

TECHNICAL FIELD

This invention relates to an imaging apparatus for use in the medicalfield, industrial field, nuclear field and so on.

BACKGROUND ART

An imaging apparatus that obtains images based on detected light orradiation has a light or radiation detector for detecting light orradiation. An X-ray detector will be described by way of example. AnX-ray detector has an X-ray converting layer (semiconductor layer) ofthe X-ray sensitive type. The X-ray conversion layer converts incident Xrays into carriers (charge information). The detector detects the X raysby reading the converted carriers. Amorphous selenium (a-Se) film, forexample, is used as the X-ray conversion layer (see Nonpatent Document1, for example).

In a radiographic operation carried out by irradiating a subject with Xrays, radiographic images transmitted through the subject are projectedonto the amorphous selenium film, thereby generating carriersproportional to the densities of the images in the film. Subsequently,the carriers generated in the film are collected by carrier collectingelectrodes in a two-dimensional arrangement. After the collection iscontinued for a predetermined time (called “storage time”), the carriersare read outside via thin-film transistors.

Such an X-ray detector has peripheral circuits such as a gate drivercircuit for turning the thin-film transistor switches on and off, and anamplifier array circuit for reading the carriers. The driver circuitapplies a driving signal to the X-ray detector to drive the X-raydetector. The amplifier array circuit receives the carriers read basedon a read signal relating to reading of the carriers. The X-ray detectorand these circuits constitute an image sensor.

For reading the carriers, there are a method of reading one line at atime through data lines, and a method of reading a plurality of linesthrough the data lines. In the case of the former method of reading oneline at a time, the thin-film transistor switches are turned on anddriven one at a time (or turned off one at a time), and carriers oncestored in capacitors connected to the switches driven are read one lineat a time through the data lines connected to the switches. In the caseof the latter method of reading a plurality of lines, on the other hand,a plurality of the thin-film transistor switches are turned on anddriven simultaneously (or two or more are turned off simultaneously),and carriers once stored in the capacitors connected to the switchesdriven simultaneously are read en bloc through the data lines connectedto these switches.

Since carriers are stored in the capacitors due to leak currents (alsocalled “dark currents”) of the amorphous selenium film even when X raysare not emitted, it is necessary to read the carriers of X-raynon-irradiation times (also called “dark image information”) by drivingthe thin-film transistors periodically. A correction is carried outbased on this dark image information read (also called “dark correction”or “offset correction”). Also for reading the dark image informationwhich consists of the carriers of non-irradiation times, either theformer method of reading one line at a time or the latter method ofreading a plurality of lines can be used.

[Nonpatent Document 1]

W. Zhao, et al., “A flat panel detector for digital radiology usingactive matrix readout of amorphous selenium,” Proc. SPIE Vol. 2708, pp.523-531, 1996.

DISCLOSURE OF THE INVENTION

[Problem to be Solved by the Invention]

The former method of reading one line at a time has a problem thatresponse is slow since the carriers are successively read one line at atime. The latter method of reading by a plurality of lines, although itcan read at higher speed than the former method of reading one line at atime, has a problem that dark image information immediately beforeirradiation cannot be acquired, and a problem that image artifacts areproduced by changing the number of the lines driven at the same time. Inany case, apart from the two techniques, it is desired to improveresponse by using a different technique.

A cause of the slow response is variations in irradiation wait time. Thevariations in irradiation wait time will be described with reference toFIG. 17. FIG. 17 is a timing chart of frame rates and signals relatingthereto in the prior art.

Frame rates T are cycles relating to a series of operations for storageand reading of carriers. During these frame rates T, carriers for framesare read (see F1-F3 for image reading in FIG. 17). Times other than theimage reading are the times when X-ray irradiation is enabled (X-rayirradiation enable times in FIG. 17). Specifically, operation is startedin the order of F1-F3 in FIG. 17. As shown in FIG. 17, assuming that thetime of image reading for each frame rate T is a “read period”, the timeother than the read period in each frame rate T is a time when X-rayirradiation is enabled. This time when X-ray irradiation is enabled iscalled “X-ray irradiation enable time”. Carrier storage for each frameis carried out in each frame rate T, including the read period and X-rayirradiation enable time. Assuming the read period to be t_(READ) and theX-ray irradiation enable time to be t_(IRRA), T=t_(READ)+t_(IRRA) isestablished as clearly seen from the reason set out above. In FIG. 17,the read period t_(READ) is set to 240 ms, and the frame rate T to 267ms.

In actually irradiating X rays, X-ray pulses are emitted during theX-ray irradiation enable times. Also at non-irradiation times beforestart of X-ray irradiation, reading for the frames usually is carriedout as shown in FIG. 17, in order to release leak currents occurring atthe non-irradiation times, and X-ray irradiation enable times t_(IRRA)are set as are irradiation times.

A hand switch is provided to make a shift to preparation for X-rayirradiation, at the non-irradiation times before start of X-rayirradiation. A shift is made to preparation for X-ray irradiation whenthe hand switch is depressed at a time A in FIG. 17. In the case of FIG.17, an X-ray irradiation enable signal is continuously outputted withoutsynchronizing with a first frame synchronization signal outputted afterthe shift to preparation for X-ray irradiation, and is stoppedsynchronously with a frame synchronization signal outputted next. As aresult, only for a period from time A to stopping of the X-rayirradiation enable signal, the X-ray irradiation enable time is longerthan the usual X-ray irradiation enable time t_(IRRA). X-ray pulses areemitted during this extended X-ray irradiation enable time.

Specifically, X-ray pulses are emitted at time B in FIG. 17, which issynchronized with the first frame synchronization signal outputted afterthe shift to preparation for X-ray irradiation, or synchronized with apredetermined time from this frame synchronization signal (thepredetermined time being less than frame rate T). The emission of X-raypulses is stopped by the time the X-ray irradiation enable signal isstopped synchronously with the frame synchronization signal outputtednext. Carriers are read for a frame (see F3 in FIG. 17) immediatelyafter the X-ray pulses are emitted, and imaging is carried out using thecarriers read. The time from time A for depressing the hand switch totime B for outputting X-ray pulses is called “irradiation wait time”.The irradiation wait time is referenced t_(WAIT).

In FIG. 17, the X-ray irradiation enable signal is continuouslyoutputted without synchronizing with the first frame synchronizationsignal outputted after the shift to preparation for X-ray irradiation,and is stopped synchronously with the frame synchronization signaloutputted next. This is not limitative. The X-ray irradiation enablesignal may be continuously outputted without synchronizing with theframe synchronization signal outputted next, and may be stoppedsynchronously with a frame synchronization signal outputted after thenext, thereby to extend the X-ray irradiation enable time and to set theemission of X-ray pulses to be long. Thus, by increasing the periodicnumber of the frame synchronization signal with which stopping of theX-ray irradiation signal is synchronized, the X-ray irradiation enabletime can be extended further to set the emission of X-ray pulses to bestill longer.

When carrying out the dark correction noted hereinbefore, as shown inFIG. 18, carriers for the frame (see the hatched frame in FIG. 18) readwith the same timing as in FIG. 17 and without outputting X-ray pulsesare read as carriers of an X-ray non-irradiation time. The darkcorrection is carried out using the read carriers as dark imageinformation. FIG. 18 is a timing chart of signals relating to reading ofdark image information in the prior art.

Specifically, as shown in FIG. 17, t refers to a storage time from startof the frame (see F2 in FIG. 17) before the frame to be imaged to startof the frame to be imaged (that is, the frame immediately after X-raypulses are outputted: see F3 in FIG. 17). The characteristic of darkimage information changes depending on the length of this storage timet. Thus, as shown in FIG. 18, a storage time from start of the framebefore the frame for reading dark image information to start of theframe for reading dark image information (see the hatched frame in FIG.18) is set to the same storage time t to be the same storage time t inFIG. 17. Although X-ray pulses are outputted between these frames inordinary imaging, X-ray pulses are not outputted when reading dark imageinformation as shown in FIG. 18.

Returning to the description of the irradiation wait time, such handswitch is depressed manually, and therefore the shift to preparation ofX-ray irradiation does not synchronize with a frame synchronizationsignal. Consequently, as shown in FIG. 19( a), for example, when thehand switch is depressed halfway through the reading for frame F2, theX-ray irradiation enable signal is continuously outputted withoutsynchronizing with the first frame synchronization signal outputtedimmediately after frame F2, and is stopped synchronously with the framesynchronization signal outputted next. X-ray pulses are outputted attime B synchronized with this frame synchronization signal orsynchronized with a predetermined time from this frame synchronizationsignal.

On the other hand, as shown in FIG. 19( b), when the hand switch isdepressed immediately after start of reading for the next frame F3, theX-ray irradiation enable signal is continuously outputted withoutsynchronizing with the first frame synchronization signal outputtedimmediately after frame F3, and is stopped synchronously with the framesynchronization signal outputted next. X-ray pulses are outputted attime B synchronized with this frame synchronization signal orsynchronized with a predetermined time from this frame synchronizationsignal.

This irradiation wait time t_(WAIT) is variable up to a maximumcorresponding to the frame rate T as shown in FIG. 19. Therefore, wherethe subject is a patient and X-ray irradiation is timed with thepatient's respiration, there occurs a problem that it is difficult tocarry out X-ray irradiation matched with respiratory timing.

This invention has been made having regard to the state of the art notedabove, and its object is to provide an imaging apparatus that canimprove response.

[Means for Solving the Problem]

To fulfill the above object, this invention provides the followingconstruction.

An imaging apparatus of this invention is an imaging apparatus forobtaining images by carrying out imaging based on light or radiation,comprising a conversion layer for converting light or radiationinformation to charge information in response to incident light orradiation, and a storage and reading circuit for storing and reading thecharge information converted by the conversion layer, the apparatusbeing constructed to obtain the images based on the charge informationread by the storage and reading circuit, the apparatus furthercomprising a first storage and readout setting device for dividing animage into a plurality of predetermined areas, and setting storage andreading of the charge information before irradiation of the light orradiation according images of the divided areas.

According to the imaging apparatus of this invention, the first storageand readout setting device divides an image into a plurality ofpredetermined areas, and sets for storage and reading of the chargeinformation before the irradiation of light or radiation to be carriedout separately according images of the divided areas. By dividing thestorage and reading of the charge information before the irradiation inthis way, when compared with the storage and reading of chargeinformation for an entire area of an image in the prior art, an averagetime for the storage and reading can be shortened to one of the numberof divisions. A time serving as a starting point of an irradiation waittime occurs before the storage and reading of the charge informationbefore the irradiation. Consequently, even if the time serving as thestarting point of the irradiation wait time varies, the variation takesplace only during each storage and reading time set short. Thus, thevariation of the irradiation wait time is made less than in the priorart, thereby improving response.

One example of the above invention (the former) provides a storage andreadout stopping device for stopping the storage and reading of thecharge information before the irradiation, even if the storage andreading of the charge information before the irradiation is only halfwaythrough an image, according to the image of a divided area correspondingto the halfway area, and an irradiation control device for controllingto carry out the irradiation after the storage and reading of the chargeinformation before the irradiation are stopped by the storage andreadout stopping device.

According to this example, even if the storage and reading of the chargeinformation before the irradiation is only halfway through an image, thestorage and readout stopping device can stop the storage and reading ofthe charge information before the irradiation according to the image ofa divided area corresponding to the halfway area. And after the storageand reading of the charge information before the irradiation are stoppedby the storage and readout stopping device, the irradiation controldevice controls to carry out the irradiation. Thus, the irradiation oflight or radiation can be carried out even when the storage and readingof the charge information before the irradiation is only halfway throughan image.

Another example of the above invention (the latter) provides a secondreadout setting device for reading the charge information before theirradiation periodically, and interposing, in an arbitrary cycle, anon-reading operation between the reading in that cycle and reading in afollowing cycle. With such second readout setting device, applicationcan be made to an imaging apparatus that carries out controlsynchronously with the cycles. The non-reading operation may be set tothe storage, or the reading and the non-reading operation may be set tothe storage.

This other example (the latter) may provide an irradiation controldevice as in the former example. That is, it provides a readout stoppingdevice for stopping the reading of the charge information before theirradiation, even if the reading of the charge information before theirradiation is only halfway through an image, according to the image ofa divided area corresponding to the halfway area, and synchronously witha cycle corresponding to halfway timing, and an irradiation controldevice for controlling to carry out the irradiation after the reading ofthe charge information before the irradiation is stopped by the readoutstopping device, and at a time of non-reading operation.

In this other example (the latter), where the irradiation control deviceis provided, even if the reading of the charge information before theirradiation is only halfway through an image, the readout stoppingdevice can stop the reading of the charge information before theirradiation according to the image of a divided area corresponding tothe halfway area. And after the reading of the charge information beforethe irradiation is stopped by the readout stopping device, and at a timeof non-reading operation, the irradiation control device controls tocarry out the irradiation. Thus, the irradiation of light or radiationcan be carried out even when the reading of the charge informationbefore the irradiation is only halfway through an image.

In the latter example, where the irradiation control device is provided,it is preferred that the reading of the charge information before theirradiation is carried out periodically in order of divided adjoiningareas, and when a last area is finished, a return is made to a firstarea for repetition. In this way, the reading of the charge informationbefore the irradiation can be repeated.

In the latter example, where the irradiation control device is provided,and in one example of repeating the reading of the charge informationbefore the irradiation, the reading of the charge information at anirradiation time is started from a next area adjacent the area where thereading of the charge information is stopped, the reading of the chargeinformation at the irradiation time is carried out periodically in theorder of the divided adjoining areas from the starting area, and whenthe last area is finished, a return is made to the first area forrepetition.

According to this example, the reading of the charge information at anirradiation time can be started from a next area adjacent the area wherethe reading of the charge information is stopped. Even if the next areawhich is an area for starting the reading of the charge information atthe irradiation time is not the first area, a return is made to thefirst area for repetition when the last area is finished. Thus, thereading of the charge area at the irradiation time can be carried outfor all the areas.

In the latter example, where the irradiation control device is provided,another example of repeating the reading of the charge informationbefore the irradiation provides an area changing device capable ofchanging areas where the reading of carriers at the irradiation time isstarted, wherein the reading of the charge information at theirradiation time is carried out periodically in the order of the dividedadjoining areas from the starting area, and when the last area isfinished, a return is made to the first area for repetition.

According to this other example, with the area changing device changingareas for starting the reading of carriers at the irradiation time, thereading of the charge information at the irradiation time can be startedfrom any arbitrary area. Even if the arbitrary area which is an area forstarting the reading of the charge information at the irradiation timeis not the first area, a return is made to the first area for repetitionwhen the last area is finished. Thus, the reading of the charge area atthe irradiation time can be carried out for all the areas.

One example of area changes by the area changing device is to start thereading of the charge information from the first area. A luminancedifference occurring at a boundary between divided images when readingthe charge information from intermediate areas can be solved by startingthe reading of the charge information at the irradiation time from thefirst area.

In the latter example, where the irradiation control device is provided,and in a further example of repeating the reading of the chargeinformation before the irradiation, the reading of the chargeinformation is carried out continuously according to all areas of theimage.

According to this further example, the reading of the charge informationat the irradiation time is carried out continuously according to all theareas of the image, whereby the reading is carried out faster than thereading of the charge information before the irradiation. As long as thestorage and reading of the charge information before the irradiation arecarried out separately in this invention, the question of response whichis the problem addressed by this invention can be solved. Thus, thereading of the charge information at the irradiation time may be carriedout continuously according to all the areas of an image.

One example of these inventions provides a correcting device forcorrecting charge information read at an irradiation time based oncharge information read at a non-irradiation time of the light orradiation. This invention is applicable where the charge information iscorrected based on the charge information read at the non-irradiationtime (dark image information). The non-irradiation time here may bebefore the irradiation noted above, or may be after the irradiation.That is, the charge information read at the non-irradiation time for usein the correction may be charge information read before the irradiation,or may be charge information read after the irradiation.

The charge information read at the non-irradiation time for use in thecorrection may consist of more than one piece. In the former and latterexamples in this invention, the start of irradiation is determined bythe time of stopping the storage and reading or stopping the reading,and the time of starting the irradiation is unknown. Therefore,considering that the time of starting the irradiation is unknown, pluralpieces of charge information matched with times of starting theirradiation are provided, thereby carrying out the above-notedcorrection with increased accuracy.

EFFECTS OF THE INVENTION

According to the imaging apparatus of this invention, a time serving asa starting point of an irradiation wait time occurs before the storageand reading of charge information before irradiation. Consequently, evenif the time serving as the starting point of the irradiation wait timevaries, the variation takes place only during each storage and readingtime set short. Thus, the variation of the irradiation wait time is madeless than in the prior art, thereby improving response.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an X-ray apparatus according to eachembodiment;

FIG. 2 shows an equivalent circuit, seen in side view, of a flat panelX-ray detector used in the X-ray apparatus;

FIG. 3 shows an equivalent circuit, seen in plan view, of the flat panelX-ray detector;

FIG. 4 is a timing chart of frame rates and signals relating theretoaccording to Embodiment 1;

FIG. 5 is a schematic view of an image divided into four;

FIGS. 6( a) and (b) are timing charts of signals before and after a handswitch is depressed in the timing chart of FIG. 4;

FIG. 7 is an explanatory view of dark image information according toEmbodiment 1;

FIG. 8 is a timing chart of frame rates and signals relating theretoaccording to Embodiment 2;

FIG. 9 is an explanatory view of dark image information according toEmbodiment 2;

FIG. 10 is a timing chart of frame rates and signals relating theretoaccording to Embodiment 3;

FIG. 11 is an explanatory view of dark image information according toEmbodiment 3;

FIG. 12 is a timing chart of frame rates and signals relating theretoaccording to Embodiment 4;

FIG. 13 is an explanatory view of dark image information according toEmbodiment 4;

FIG. 14 is a timing chart of frame rates and signals relating theretoaccording to a modification.

FIG. 15 is a schematic view of an image dividing mode according to afurther modification;

FIG. 16 is a timing chart of frame rates and signals relating theretoaccording to the further modification;

FIG. 17 is a timing chart of frame rates and signals relating thereto inthe prior art;

FIG. 18 is a timing chart of signals relating to reading of dark imageinformation in the prior art; and

FIGS. 19( a) and (b) are timing charts of signals before and after ahand switch is depressed in the timing chart of FIG. 17.

DESCRIPTION OF REFERENCES

7 . . . X-ray tube controller

8 . . . analog-to-digital converter

9 . . . image processor

10 . . . controller

31 . . . semiconductor thick film

37 . . . amplifier array circuit

Ca . . . capacitors

D1, D2, D3, D4 . . . areas

t_(READ) . . . read period

T . . . frame rates

S . . . image sensor

Embodiment 1

Embodiment 1 of this invention will be described hereinafter withreference to the drawings. FIG. 1 is a block diagram of an X-rayapparatus according to each embodiment. FIG. 2 is an equivalent circuit,seen in side view, of a flat panel X-ray detector used in the X-rayapparatus. FIG. 3 is an equivalent circuit, seen in plan view, of theflat panel X-ray detector. Embodiment 1, including Embodiments 2-4 tofollow, will be described, taking the flat panel X-ray detector(hereinafter called “FPD” as appropriate) as an example of light orradiation detector, and the X-ray apparatus as an example of imagingapparatus. The X-ray apparatus and FPD in each embodiment areconstructed as shown in FIGS. 1-3.

As shown in FIG. 1, the X-ray apparatus according to Embodiment 1,including Embodiments 2-4 to follow, has an X-ray tube 2 for emitting Xrays toward a patient M, and an FPD 3 for detecting X rays transmittedthrough the patient M.

The X-ray apparatus further includes an FPD controller 5 for controllingscanning action of the FPD 3, an X-ray tube controller 7 having a highvoltage generator 6 for generating a tube voltage and tube current forthe X-ray tube 2, an analog-to-digital converter 8 for fetching X-raydetection signals which are charge signals from the FPD 3 and digitizingthe signals, an image processor 9 for performing various processes basedon the X-ray detection signals outputted from the analog-to-digitalconverter 8, a controller for performing an overall control of thesecomponents, a memory 11 for storing processed images, an input unit 12for the operator to input settings, and a monitor 13 for displaying theprocessed images and the like.

The FPD controller 5 controls scanning action by moving the FPD 3horizontally or revolving the FPD 3 about the body axis of patient M.The high voltage generator 6 generates the tube voltage and tube currentfor the X-ray tube 2 to emit X rays. The X-ray tube controller 7controls scanning action by moving the X-ray tube 2 horizontally orrevolving the X-ray tube 2 about the body axis of patient M, andcontrols setting of a coverage of a collimator (not shown) disposedadjacent the X-ray tube 2. In time of scanning action of the X-ray tube2 and FPD 3, the X-ray tube 2 and FPD 3 are moved while maintaining amutually opposed relationship, so that the FPD 3 may detect X raysemitted from the X-ray tube 2.

The controller 10 has a central processing unit (CPU) and otherelements. The memory 11 has storage media, typically a ROM (Read-OnlyMemory) and a RAM (Random Access Memory). The input unit 12 has apointing device, typically a mouse, keyboard, joy stick, trackballand/or touch panel. The X-ray apparatus creates images of the patient M,with the FPD 3 detecting X rays transmitted through the patient M, andthe image processor 9 performing an image processing based on the X raysdetected.

In Embodiment 1, the controller 10 has also a function, describedhereinafter, to divide an image equally into four areas D1-D4 (see FIG.5), and set for reading of carriers before irradiation separatelyaccording to images of the four divided areas D1-D4. Further, thecontroller 10 has also (1) a function to read carriers beforeirradiation periodically, and interpose, in an arbitrary cycle, anon-reading operation (X-ray irradiation enable in FIG. 4) betweenreading in that cycle and reading in the following cycle, and (2) afunction to stop the reading of carriers before the irradiation, even ifthe reading of carriers before the irradiation is only halfway throughan image, according to the image of a divided area (D2 in FIG. 4)corresponding to the halfway area, and synchronously with the cyclecorresponding to the halfway timing. The controller 10 corresponds tothe first storage and readout setting device, the second readout settingdevice and the readout stopping device in this invention.

In Embodiment 1, the X-ray tube controller 7 has a function to controlthe X-ray tube 2 to emit X rays after the reading of carriers before theirradiation is stopped halfway through an image and at the time ofnon-reading operation (X-ray irradiation enable). The X rays emittedfrom the X-ray tube 2 at this time are X-ray pulses. The X-ray tubecontroller 7 corresponds to the irradiation control device in thisinvention.

Regarding the memory 11, the RAM is used for writing of X-ray detectionsignals, processed images and so on, and the ROM is used for readingonly of a program of control sequence when, for example, causing thecontroller 10 to perform the control sequence by reading the program ofcontrol sequence. Embodiment 1, including also Embodiments 2-4 tofollow, causes the memory 11 to store the program of control sequencewhich sets for reading of carriers before the irradiation separatelyaccording to images of the four divided areas D1-D4, and causes thecontroller 10 to perform the control sequence by reading the program.

In Embodiment 1, including also Embodiments 2-4 to follow, the inputunit 12 has a hand switch (not shown), and has a function to make ashift to preparation for X-ray irradiation by depressing the handswitch, and start X-ray irradiation after lapse of a predetermined time.Specifically, as shown in FIG. 4, a shift is made to preparation forX-ray irradiation when the hand switch is depressed at time A, and anX-ray irradiation enable signal is continuously outputted withoutsynchronizing with a first frame synchronization signal outputted, andis stopped synchronously with a frame synchronization signal outputtednext. X-ray pulses are emitted while the X-ray irradiation enable signalis outputted.

As shown in FIG. 2, the FPD 3 includes a radiation sensitive thicksemiconductor film 31 for generating carriers in response to incidentradiation such as X rays, a voltage application electrode 32 formed onthe surface of thick semiconductor film 31, carrier collectingelectrodes 33 arranged on the back surface remote from the radiationincidence side of the thick semiconductor film 31, carrier storingcapacitors Ca for storing the carriers collected by the carriercollecting electrodes 33, and thin-film transistors (TFT) Tr acting ascharge fetching switching elements, normally turned off (cutoff), forfetching the carriers (charges) from the capacitors Ca. In Embodiment 1,including also Embodiments 2-4 to follow, the thick semiconductor film31 is formed of a radiation sensitive material which generates carriersin response to incident radiation, such as amorphous selenium, but maybe formed of a light sensitive material for generating carriers inresponse to incident light. The thick semiconductor film 31 correspondsto the conversion layer in this invention.

In addition, Embodiment 1, including also Embodiments 2-4 to follow,provides data lines 34 connected to the sources of the thin-filmtransistors Tr, and gate lines 35 connected to the gates of thethin-film transistors Tr. The voltage application electrode 32, thicksemiconductor film 31, carrier collecting electrodes 33, capacitors Ca,thin-film transistors Tr, data lines 34 and gate lines 35 are laminatedon an insulating substrate 36.

As shown in FIGS. 2 and 3, the capacitors Ca and thin-film transistorsTr are connected, respectively, to the numerous (e.g. 1,024×1,024 or4,096×4,096) carrier collecting electrodes 33 arranged in atwo-dimensional matrix of rows and columns. Each set of carriercollecting electrode 33, capacitor Ca and thin-film transistor Tr actsas a separate detecting element DU. The voltage application electrode 32is formed over the entire surface as a common electrode of all thedetecting elements DU. As shown in FIG. 3, the data lines 34 form aplurality of columns juxtaposed in the horizontal (X) direction, while,as shown in FIG. 3, the gate lines 35 form a plurality of rowsjuxtaposed in the vertical (Y) direction. Each data line 34 and eachgate line 35 are connected to the detecting elements DU. The data lines34 are connected to an amplifier array circuit 37. The gate lines 35 areconnected to a gate driver circuit 38. The number of detecting elementsDU is not limited to 1,024×1,024 or 4,096×4,096, but is variableaccording to forms of implementation. Thus, only one detecting elementDU may be provided.

The detecting elements DU are patterned in the two-dimensional matrixarrangement on the insulating substrate 36. The insulating substrate 36having the detecting elements DU patterned thereon is also called“active matrix substrate”.

For forming the detecting elements DU and adjacent components of FPD 3,the data lines 34 and gate lines 35 are wired, and the thin-filmtransistors Tr, capacitors Ca, carrier collecting electrodes 33, thicksemiconductor film 31 and voltage application electrode 32 aresuccessively laminated on the surface of the insulating substrate 36 byusing a thin-film formation technique based on a varied vacuumdeposition method or photolithographic patterning. The semiconductor forforming the thick semiconductor film 31 may be selected appropriatelyaccording to use and withstand voltage, as exemplified by amorphoussemiconductor and polycrystallized semiconductor.

The amplifier array circuit 37, including the analog-to-digitalconverter 8 disposed externally of the FPD 3, has a function to receivethe carriers. That is, the analog-to-digital converter 8 and amplifierarray circuit 37 read, through the detecting elements DU of the FPD 3,the carriers converted by the semiconductor thick film 31. Thecapacitors Ca correspond to the storage circuits in this invention. Theanalog-to-digital converter 8 and amplifier array circuit 37 correspondto the reading circuits in this invention. Thus, the image sensor Sincluding the capacitors Ca, analog-to-digital converter 8 and amplifierarray circuit 37 corresponds to the storage and reading circuit in thisinvention. The analog-to-digital converter 8 may be included in theconstruction of FPD 3. These gate driver circuit 38, amplifier arraycircuit 37 and analog-to-digital converter 8 are the peripheral circuitsof the FPD 3.

In addition, the FPD 3 has a power source 39. In Embodiment 1, includingalso Embodiments 2-4 to follow, the power source 39 supplies electricpower to the reading circuits, such as the amplifier array circuit 37and analog-to-digital converter 8. The FPD 3, FPD controller 5 andanalog-to-digital converter 8 constitute the image sensor S in FIG. 3.

Next, operation of the X-ray apparatus and flat panel X-ray detector(FPD) in Embodiment 1, including also Embodiments 2-4 to follow, will bedescribed. Radiation to be detected is emitted in the state of a highbias voltage V_(A) (e.g. several hundred volts to several tens ofkilovolts) being applied to the voltage application electrode 32. Thisbias voltage V_(A) is applied also under control of the FPD controller5.

Carriers are generated by incidence of the radiation, and are stored ascharge information in the charge-storing capacitors Ca. A gate line 35is selected by a signal-fetching scan signal (i.e. gate driving signal)to the gate driver circuit 38. Further, the detecting elements DUconnected to this gate line 35 are designated. The carriers (charges)stored in the capacitors Ca of the designated detecting elements DU areoutputted to the data lines 34 via the thin-film transistors Tr turnedon by the signal on the selected gate line 35.

The address of each detecting element DU is designated based on thesignal fetching scan signals on the data line 34 and gate line 35 (i.e.the gate driving signal on the gate line 35 and amplifier driving signalon the data line 34). When a signal fetching scan signal is inputted tothe amplifier array circuit 37 and gate driver circuit 38, eachdetecting element DU is selected by a scan signal (gate driving signal)of the vertical (Y) direction outputted from the gate driver circuit 38.Then, the amplifier array circuit 37 is switched by a scan signal of thehorizontal (X) direction (amplifier driving signal), whereby thecarriers (charges) from the capacitor Ca of a selected detecting elementDU are outputted to the amplifier array circuit 37 through the data line34. The charges are amplified by the amplifier array circuit 37, andoutputted as X-ray detection signals from the amplifier array circuit 37to the analog-to-digital converter 8.

Where the image sensor S having the FPD 3 in Embodiment 1 is used in theX-ray apparatus for detecting X-ray images, for example, the aboveoperation causes the amplifier array circuit 37 to amplify chargeinformation (X-ray detection signals) read through the data lines 34 asvoltages, convert it to image information and output it as an X-rayimage. Thus, the X-ray apparatus is constructed to obtain X-ray imagesbased on the charge information (X-ray detection signals) stored in andread from the image sensor S including the capacitors Ca,analog-to-digital converter 8 and amplifier array circuit 37.

Next, the division of an image, setting for reading, and signalsrelating to each frame rate according to Embodiment 1, will be describedwith reference to FIGS. 4-6. FIG. 4 is a timing chart of frame rates andsignals relating thereto according to Embodiment 1. FIG. 5 is aschematic view of an image divided into four. FIG. 6 shows timing chartsof signals before and after the hand switch is depressed in the timingchart of FIG. 4.

As noted in the “Background Art” section, frame rates T are cyclesrelating to a series of operations for storage and reading of carriers.During these frame rates T, carriers for frames are read (see D1-D4 inFIG. 4). Times other than the image reading are the times when X-rayirradiation is enabled (X-ray irradiation enable times in FIG. 4).Specifically, as shown in FIG. 4, reading is started in the order ofD1-D4 synchronously with a frame synchronization signal outputted foreach frame rate T. Here, an X-ray image is divided equally into fourareas D1, D2, D3 and D4 along the gate lines 35 as shown in FIG. 5. Thecontroller 10 sets for the carriers to be read separately according tothe divided areas D1-D4. Assuming that D1 is the first area and D4 thelast area, when (carrier reading for) the last area D4 is finished, theoperation returns to the first area D1 to repeat the reading. That is,the carriers are read periodically in the order of the divided adjoiningareas, and when the last area D4 is finished, the operation returns tothe first area D1 to repeat the reading.

As shown in FIG. 4, assuming that the time of image reading for eachframe rate T is a “read period”, the time other than the read period ineach frame rate T is a time when X-ray irradiation is enabled. This timewhen X-ray irradiation is enabled is called “X-ray irradiation enabletime”. Carrier storage for each frame is carried out in each frame rateT, including the read period and X-ray irradiation enable time. Assumingthe read period to be t_(READ) and the X-ray irradiation enable time tobe t_(IRRA), T=t_(READ)+t_(IRRA) is established as clearly seen from thereason set out above. In FIG. 4, the read period t_(READ) is set to 60ms, and the frame rate T to 66 ms. Conventionally, as shown in FIG. 17,the read period t_(READ) has been 240 ms, and the frame rate T 267 ms.The read period t_(READ) can be set as short as one fourth of that inthe prior art, correspondingly to the division of an image into fourareas (here, 240 ms×¼=60 ms). As a result, the frame rate T can also bereduced (here, from 267 ms to 66 ms).

In actually emitting X rays, X-ray pulses are emitted during the X-rayirradiation enable times. Also at non-irradiation times before start ofX-ray irradiation, carriers are usually read for the divided areas asshown in FIG. 4, in order to release leak currents occurring at thenon-irradiation times, and X-ray irradiation enable times t_(IRRA) areset as are irradiation times.

At a non-irradiation time before start of X-ray irradiation, the handswitch is depressed at time A in FIG. 4 to make a shift to preparationfor the X-ray irradiation. The depression of the hand switch results ina shift to preparation for the X-ray irradiation. In the case of FIG. 4,the X-ray irradiation enable signal is continuously outputted withoutsynchronizing with a first frame synchronization signal outputted afterthe shift to preparation for the X-ray irradiation, and is stoppedsynchronously with a frame synchronization signal outputted next. As aresult, only for a period from time A to stopping of the X-rayirradiation enable signal, the X-ray irradiation enable time is longerthan the usual X-ray irradiation enable time t_(IRRA). X-ray pulses areemitted during this extended X-ray irradiation enable time.

Specifically, X-ray pulses are emitted at time B in FIG. 4, which issynchronized with the first frame synchronization signal outputted afterthe shift to preparation for X-ray irradiation, or synchronized with apredetermined time from this frame synchronization signal. The emissionof X-ray pulses is stopped by the time the X-ray irradiation enablesignal is stopped synchronously with the frame synchronization signaloutputted next. Carriers are read for an area (see D3 in FIG. 4)immediately after the X-ray pulses are emitted, reading is carried outfor the respective areas (see D4, D1 and D2 in FIG. 4) until thecarriers are read for the entire area of the image, and imaging iscarried out using the carriers read. The time from time A for depressingthe hand switch to time B for outputting the X-ray pulses is called“irradiation wait time”. The irradiation wait time is referencedt_(WAIT).

Since such hand switch is depressed manually, the shift to preparationfor X-ray irradiation does not synchronize with a frame synchronizationsignal. Therefore, as shown in FIG. 6( a), for example, when the handswitch is depressed halfway through reading for area D2, the X-rayirradiation enable signal is continuously outputted withoutsynchronizing with a first frame synchronization signal outputtedimmediately after the area D2, and is stopped synchronously with a framesynchronization signal outputted next. X-ray pulses are outputted attime B, which is synchronized with this frame synchronization signal, orsynchronized with a predetermined time from the frame synchronizationsignal.

On the other hand, when, as shown in FIG. 6( b), the hand switch isdepressed immediately after start of reading for the next area D3, theX-ray irradiation enable signal is continuously outputted withoutsynchronizing with a first frame synchronization signal outputtedimmediately after the area D3, and is stopped synchronously with a framesynchronization signal outputted next. X-ray pulses are outputted attime B, which is synchronized with this frame synchronization signal, orsynchronized with a predetermined time from the frame synchronizationsignal.

The irradiation wait time t_(WAIT) is variable up to a maximumcorresponding to the frame rate T as shown in FIG. 6. In Embodiment 1,the variation is reduced to the frame rate T of 66 ms set as short asapproximately one fourth of the variation corresponding to the framerate T of 267 ms in the prior art.

With the X-ray apparatus according to Embodiment 1 described above, thecontroller 10 divides an image into a plurality of predetermined areas(divides an image equally into four areas D1-D4 in FIG. 5), and sets forreading of carriers before irradiation separately according to images ofthe divided areas (four areas D1-D4 in FIGS. 4 and 6). By dividing thereading of carriers before the irradiation in this way, when comparedwith the reading of carriers for all areas of an image (i.e. a frame) inthe prior art, the read period t_(READ) or each frame rate T can beshortened to one of the number of divisions (one fourth in FIGS. 4-6).The time serving as the starting point of irradiation wait time t_(WAIT)(time A at which the hand switch is depressed in Embodiment 1) occursbefore the reading of carriers before the irradiation. Even if the timeserving as the starting point of irradiation wait time t_(WAIT) varies,the variation takes place only during each read period t_(READ) or eachframe rate T set short. Therefore, the variation in irradiation waittime t_(WAIT) is made less than in the prior art, thereby improvingresponse.

In FIG. 4, the controller 10 (see FIG. 1) sets for reading of carriersbefore the irradiation to be carried out periodically, and interposes,in an arbitrary cycle, a non-reading operation (X-ray irradiation enablein FIG. 4) between reading in that cycle and reading in the followingcycle. Such controller 10 is applicable to an imaging apparatus whichperforms controls synchronously with cycles. In FIG. 4, the non-readingoperation (X-ray irradiation enable) may be set to the storage ofcarriers, or the reading and the non-reading operation (X-rayirradiation enable) may be set to the storage of carriers.

In FIG. 4, the controller 10 (see FIG. 1) sets for stopping the readingof carriers before the irradiation, even if the reading of carriersbefore the irradiation is only halfway through an image, according tothe image of a divided area (D2 in FIG. 4) corresponding to the halfwayarea, and synchronously with the cycle corresponding to the halfwaytiming. The X-ray tube controller 7 (see FIG. 1) controls the X-ray tube2 to emit X rays after the reading of carriers before the irradiation isstopped by the controller 10 and at the time of non-reading operation(X-ray irradiation enable).

With such X-ray tube controller 7 provided, the reading of carriersbefore the irradiation can be stopped by the controller 10, even if thereading of carriers before the irradiation is only halfway through animage, according to the image of a divided area (D2 in FIG. 4)corresponding to the halfway area. And, the X-ray tube controller 7controls the X-ray tube 1 (see FIG. 1) to emit X rays after the readingof carriers before the irradiation is stopped by the controller 10 andat the time of non-reading operation (X-ray irradiation enable). Thus, Xrays can be emitted even if the reading of carriers before theirradiation is only halfway through an image.

In FIG. 4, the reading of carriers before the irradiation is carried outperiodically in the order of divided adjoining areas (the order of D1,D2, D3 and D4 in FIG. 4), and when carrier reading for the last area (D4in FIG. 4) is finished, the operation returns to the first area (D1 inFIG. 4) to repeat the reading. The carriers can be read before theirradiation in this way.

In FIG. 4, the reading of carriers at an irradiation time is startedfrom the next area (D3 in FIG. 4) adjacent the area (D2 in FIG. 4) wherethe above carrier reading is stopped. The reading of carriers at theirradiation time is carried out periodically in the order of the dividedadjoining area (the order of D4 in FIG. 4) from the starting area (D3 inFIG. 4). When the last area (D4 in FIG. 4) is finished, the operationreturns to the first area (D1 in FIG. 4) to repeat the reading.

In this way, the reading of carriers at the irradiation time can bestarted from the next area (D3 in FIG. 4) adjacent the area (D2 in FIG.4) where the carrier reading is stopped. Even if the next area (D3 inFIG. 4) which is the area where the reading of carriers at theirradiation time is started is not the first area (D1 in FIG. 4) asshown in FIG. 4, the operation returns to the first area (D1 in FIG. 4)when the last area (D4 in FIG. 4) is finished, to repeat the reading.Thus, the reading of carriers at the irradiation time can be carried outover all areas. That is, image reading can be carried out over all theareas of the image, for imaging.

In Embodiment 1, including also Embodiments 2-4 to follow, the imageprocessor 9 (see FIG. 1) has a function to correct the carriers read atthe irradiation time, based on the carriers read at the non-irradiationtime. This invention can be applied where charge information iscorrected (dark correction) based on the carriers read at thenon-irradiation time (dark image information). The image processor 9corresponds to the correcting device in this invention.

In Embodiment 1, including also Embodiments 2-4 to follow, carriers areread before the irradiation as noted above, that is leak currents areread beforehand, and the leak currents read are once stored and writtenas dark image information in the memory 11 (see FIG. 1) through theanalog-to-digital converter 8, image processor 9 and controller 10 (seeFIG. 1 for all). Subsequently, the carriers read at the irradiation timeare once stored and written as X-ray detection signals in the memory 11(see FIG. 1) through the analog-to-digital converter 8, image processor9 and controller 10 (see FIG. 1 for all). At a time of dark correctionby the image processor 9, the dark image information and X-ray detectionsignals written in the memory 11 are read, the dark correction iscarried out through a correction process such as of subtracting the darkimage information from the X-ray detection signals, and the data afterthe dark correction is once stored and written as an X-ray image in thememory 11. This X-ray image after the dark correction is outputted toand displayed on the monitor 13 (see FIG. 1), for example. To summarizethe above, the dark image information read at the non-irradiation timeand used in the correction consists of the carriers read before theirradiation in Embodiment 1.

The case of applying this dark image information to the timing chart ofFIG. 4 as in Embodiment 1 will be described with reference to FIG. 7.FIG. 7 is an explanatory view of the dark image information according toEmbodiment 1. In carrying out the dark correction, as shown in FIG. 7,the carriers for areas read with the same timing as in FIG. 4 andwithout outputting X-ray pulses are read as carriers at the X-raynon-irradiation time. The dark correction is carried out by using thecarriers read as dark image information.

In FIG. 4, the reading of carriers before the irradiation is carried outperiodically in the order of divided adjoining areas (the order of D1,D2, D3 and D4 in FIG. 4), and when carrier reading for the last area (D4in FIG. 4) is finished, the operation returns to the first area (D1 inFIG. 4) to repeat the reading. And, even if the reading of carriersbefore the irradiation is only halfway through an image, the reading ofcarriers before the irradiation is stopped according to the image of adivided area corresponding to the halfway area. And, the reading ofcarriers at the irradiation time is started from the next area adjacentthe area where the carrier reading is stopped. The reading of carriersat the irradiation time is carried out periodically in the order of thedivided adjoining areas from the starting area. When the last area isfinished, the operation returns to the first area to repeat the reading.Therefore, when an image is divided equally into four areas D1-D4, thereading takes four patterns P1, P2, P3 and P4 as shown in FIG. 7.

Specifically, in pattern P1, carriers are read before the irradiation inthe order of areas D1, D2, D3 and D4, and carriers are read at theirradiation time in the order of areas D1, D2, D3 and D4. In pattern P2,carriers are read before the irradiation in the order of areas D2, D3,D4 and D1, and carriers are read at the irradiation time in the order ofareas D2, D3, D4 and D1. In pattern P3, carriers are read before theirradiation in the order of areas D3, D4, D1 and D2, and carriers areread at the irradiation time in the order of areas D3, D4, D1 and D2. Inpattern P4, carriers are read before the irradiation in the order ofareas D4, D1, D2 and D3, and carriers are read at the irradiation timein the order of areas D4, D1, D2 and D3.

A storage time from start of a previous area identical to an area to beimaged to start of the area to be imaged is referred to as ti for areaD1, t₂ for area D2, t₃ for area D3 and t₄ for area D4 (see FIGS. 4 and7). Storage times t₁, t₂, t₃ and t₄ for the respective areas, whenexpressed in terms of frame rate T, are t₁=t₂=t₃=t₄=5×T in all patternsP1-P4, as shown in FIG. 7.

The characteristics of dark image information will change depending onthe length of storage times t₁, t₂, t₃ and t₄. Thus, when, as shown inFIG. 4, images are processed by carrying out the reading of carriersbefore the irradiation in the order of areas D3, D4, D1 and D2 and thereading of carries at the irradiation time in the order of areas D3, D4,D1 and D2, the imaging will be in a pattern corresponding to pattern P3.Normally, it is ideal to carry out the dark correction using thecarriers (dark image information) read before the irradiation in patternP3. However, since t₁=t₂=t₃=t₄=5×T applies commonly to all patternsP1-P4 in Embodiment 1 as noted above, the dark correction may be carriedout using the carriers (dark image information) read before theirradiation in a pattern applicable any one of the patterns P1-P4.

To summarize the above, in Embodiment 1, the reading of carriers beforethe irradiation is carried out periodically in the order of the dividedadjoining areas, and when the carrier reading for the last area isfinished, the operation returns to the first area to repeat the reading.Even if the reading of carriers before the irradiation is only halfwaythrough an image, the reading of carriers before the irradiation isstopped according to the image of a divided area corresponding to thehalfway area. The reading of carriers at the irradiation time is startedfrom the next area adjacent the area where the carrier reading isstopped. The reading of carriers at the irradiation time is carried outperiodically in the order of the divided adjoining areas from thestarting area. When the last area is finished, the operation returns tothe first area to repeat the reading. The dark correction can be carriedout accurately only with one piece of dark image information.

Embodiment 2

Next, Embodiment 2 of this invention will be described with reference tothe drawings. FIG. 8 is a timing chart of frame rates and signalsrelating thereto according to Embodiment 2. The X-ray apparatus and FPDin Embodiment 2 have the same constructions as in Embodiment 1 describedabove. Thus, their description will be omitted, and only the differencewill be described.

The difference to Embodiment 1 lies in that the controller 10 (seeFIG. 1) has an area changing function for changing areas where thereading of carriers at the irradiation time is started. However, as inEmbodiment 1, the reading of carriers at the irradiation time is carriedout periodically in the order of the divided adjoining areas from thestarting area, and when the last area (D4 in FIG. 8) is finished, theoperation returns to the first area (D1 in FIG. 8) to repeat thereading. The following description will be made on an assumption that,in Embodiment 2, the reading of carriers at the irradiation time isstarted from the first area (D1 in FIG. 8). The controller 10 inEmbodiment 2 corresponds to the first storage and readout settingdevice, the second readout setting device, the readout stopping deviceand the area changing device in this invention.

Specifically, as shown in FIG. 8, the reading of carriers before theirradiation is carried out in the order of areas D3, D4, D1 and D2, andthe area for starting the reading of carriers at the irradiation time ischanged to the first area D1. And the reading of carriers at theirradiation time is carried out periodically in the order of the dividedadjoining areas (D2, D3 and D4 in FIG. 8) from the starting area D1.

With the X-ray apparatus according to Embodiment 2 described above, thecontroller 10 changes the area for starting the reading of carriers atthe irradiation time, and thus it is possible to select an arbitraryarea for starting the reading of carriers at the irradiation time. InEmbodiment 2, the arbitrary area for starting the reading of carriers atthe irradiation time is the first area (D1 in FIG. 8). Even if this isnot the first area, the reading of carriers at the irradiation time canbe carried out over all areas since the operation returns to the firstarea (D1 in FIG. 8) when the last area (D4 in FIG. 8) is finished, torepeat the reading.

In Embodiment 2, the area for starting the reading of carriers at theirradiation time is changed to the first area, such that the reading ofcarriers at the irradiation time is started from the first area (D1 inFIG. 8). However, as noted above, the area for starting the reading ofcarriers at the irradiation time is not limited to the first area, butmay be any arbitrary area.

Where, as in Embodiment 1 described hereinbefore, the reading ofcarriers at the irradiation time is started from the next area (D3 inFIG. 4) adjacent the area (D2 in FIG. 4) where the carrier reading hasstopped, a luminance difference occurs between area D2 and area D3divided when reading carriers. In Embodiment 2, the luminance differenceoccurring at the boundary between divided images when reading carriersfrom such intermediate areas can be solved by starting the reading ofcarriers at the irradiation time from the first area.

The case of applying the dark image information to the timing chart ofFIG. 8 as in Embodiment 2 will be described with reference to FIG. 9.FIG. 9 is an explanatory view of the dark image information according toEmbodiment 2. In carrying out a dark correction, as shown in FIG. 9, thecarriers for areas read with the same timing as in FIG. 8 and withoutoutputting X-ray pulses are read as carriers at the X-raynon-irradiation time. The dark correction is carried out by using thecarriers read as dark image information. In this case, the reading takesfour patterns P1, P2, P3 and P4 as shown in FIG. 9.

Specifically, in pattern P1, carriers are read before the irradiation inthe order of areas D1, D2, D3 and D4, and carriers are read at theirradiation time in the order of areas D1, D2, D3 and D4. In pattern P2,carriers are read before the irradiation in the order of areas D2, D3,D4 and D1, and carriers are read at the irradiation time in the order ofareas D1, D2, D3 and D4. In pattern P3, carriers are read before theirradiation in the order of areas D3, D4, D1 and D2, and carriers areread at the irradiation time in the order of areas D1, D2, D3 and D4. Inpattern P4, carriers are read before the irradiation in the order ofareas D4, D1, D2 and D3, and carriers are read at the irradiation timein the order of areas D1, D2, D3 and D4.

As in Embodiment 1, a storage time from start of a previous area,identical to an area to be imaged, to start of the area to be imaged isreferred to as t₁ for area D1, t₂ for area D2, t₃ for area D3 and t₄ forarea D4. Storage times ti, t₂, t₃ and t₄ for the respective areas, whenexpressed in terms of frame rate T, are as follows, as shown in FIG. 9.

In pattern P1, t₁=5×T, t₂−5×T, t₃=5×T and t₄=5×T. In pattern P2, t₁−2×T,t₂×6×T, t₃=6×T and t₄−6×T. In pattern P3, t₁−3×T, t₂=3×T, t₃=7×T andt₄−7×T. In pattern P4, t₁=4×T, t₂=4×T, t₃=4×T and t₄−8×T.

As noted in Embodiment 1, the characteristics of dark image informationwill change depending on the length of storage times t₁, t₂, t₃ and t₄.Thus, when, as shown in FIG. 8, images are processed by carrying out thereading of carriers before the irradiation in the order of areas D3, D4,D1 and D2, and the area for starting the reading of carriers at theirradiation time is changed to area D1 to carry out the reading ofcarries at the irradiation time in the order of areas D1, D2, D3 and D4,the images will be in a pattern corresponding to pattern P3. Thus, it isideal carry out the dark correction using the carriers (dark imageinformation) read before the irradiation in pattern P3.

In Embodiment 2, as distinct from Embodiment 1 described hereinbefore,the storages times t₁, t₂, t₃ and t₄ for the respective patterns P1-P4are different from one another, and the characteristics of the darkimage information are different. It is therefore desirable to haveplural pieces of dark image information for the respective patterns(four patterns P1-P4 in this case). The start of irradiation isdetermined by the time of stopping the storage and reading or stoppingthe reading (which is time A of depressing the hand switch in thiscase), and the time of starting irradiation is unknown. That is,depending on the time, imaging can be in a pattern corresponding to eachof patterns P1-P4. Therefore, considering that the time of startingirradiation is unknown, plural pieces of dark image information matchedwith times of starting irradiation are provided, thereby carrying outthe dark correction with increased accuracy.

Embodiment 3

Next, Embodiment 3 of this invention will be described with reference tothe drawings. FIG. 10 is a timing chart of frame rates and signalsrelating thereto according to Embodiment 3. The X-ray apparatus and FPDin Embodiment 3 have the same constructions as in Embodiments 1 and 2described above. Thus, their description will be omitted, and only thedifference will be described.

The difference to Embodiments 1 and 2 lies in that the reading ofcarriers at the irradiation time is carried out continuously accordingto all the areas of an image. The reading of carriers before theirradiation is the same as in Embodiments 1 and 2 in that it is carriedout periodically in the order of the divided adjoining areas (in theorder of D1, D2, D3 and D4 in FIG. 10), and when the reading of carriersfor the last area (D4 in FIG. 10) is finished, the operation returns tothe first area (D1 in FIG. 10) to repeat the reading.

Specifically, as shown in FIG. 10, the reading of carriers before theirradiation is carried out in the order of areas D3, D4, D1 and D2, andthe reading of carriers at the irradiation time is carried outcontinuously according to all the areas of the image. This is carriedout continuously in the order of areas D3, D4, D1 and D2. Consequently,compared with the frame rate before the irradiation, the frame rateafter the irradiation becomes long as does the frame rate in the priorart. When the frame rate before the irradiation is T₁ and the frame rateafter the irradiation is T₂, T₁ becomes 66 ms, and T₂ 267 ms.

With the X-ray apparatus according to Embodiment 3 described above, thereading of carriers at the irradiation time is carried out continuouslyaccording to all the areas of an image, whereby the reading is carriedout faster than the carrier reading before the irradiation. In the caseof FIG. 10, since the X-ray irradiation enable times are omitted duringthe irradiation, the reading can be carried out at a correspondinglyincreased speed. As long as the storage and reading of carriers beforethe irradiation are carried out separately in this invention, thequestion of response which is the problem addressed by this inventioncan be solved. In Embodiment 3 and in Embodiment 4 to follow, thereading of carriers at the irradiation time may be carried outcontinuously according to all the areas of an image.

The case of applying the dark image information to the timing chart ofFIG. 10 as in Embodiment 3 will be described with reference to FIG. 11.FIG. 11 is an explanatory view of the dark image information accordingto Embodiment 3. In carrying out a dark correction, as shown in FIG. 11,the carriers for the areas read with the same timing as in FIG. 10 andwithout outputting X-ray pulses are read as carriers at the X-raynon-irradiation time. The dark correction is carried out by using thecarriers read as dark image information. In this case, the reading takesfour patterns P1, P2, P3 and P4 as shown in FIG. 11.

Specifically, in pattern P1, carriers are read before the irradiationseparately in the order of areas D1, D2, D3 and D4, and carriers areread at the irradiation time continuously in the order of areas D1, D2,D3 and D4. In pattern P2, carriers are read before the irradiationseparately in the order of areas D2, D3, D4 and D1, and carriers areread at the irradiation time continuously in the order of areas D2, D3,D4 and D1. In pattern P3, carriers are read before the irradiationseparately in the order of areas D3, D4, D1 and D2, and carriers areread at the irradiation time in the order of areas D3, D4, D1 and D2. Inpattern P4, carriers are read before the irradiation separately in theorder of areas D4, D1, D2 and D3, and carriers are read at theirradiation time continuously in the order of areas D4, D1, D2 and D3.

As in Embodiments 1 and 2, a storage time from start of a previous area,identical to an area to be imaged, to start of the area to be imaged isreferred to as t₁ for area D1, t₂ for area D2, t₃ for area D3 and t₄ forarea D4. Storage times t₁, t₂, t₃ and t₄ for the respective areas, whenexpressed in terms of frame rate T and read period t_(READ), are asfollows, as shown in FIG. 11.

In pattern P1, t₁=5×T₁, t₂=4×T₁+t_(READ), t₃=3×T₁+2×t_(READ) andt₄=2×T₁+3×t_(READ). In pattern P2, t₁=2×T₁+3×t_(READ), t₂−5×T₁,t₃=4×T₁+t_(READ) and t₄=3×T₁+2>t_(READ). In pattern P3,t₁=3×T₁+2×t_(READ), t₂=2×T₁+3×t_(READ), t₃=5×T₁ and t₄−4×T₁+t_(READ). Inpattern P4, t₁=4×T₁+t_(READ), t₂=3×T₁+2×t_(READ), t₃=2×T₁+3×t_(READ) andt₄=5×T₁.

As noted in Embodiments 1 and 2, the characteristics of dark imageinformation will change depending on the length of storage times t₁, t₂,t₃ and t₄. Thus, when, as shown in FIG. 10, images are processed bycarrying out the reading of carriers before the irradiation separatelyin the order of areas D3, D4, D1 and D2, and the reading of carries atthe irradiation time is carried out continuously in the order of areasD3, D4, D1 and D2, the imaging will be in a pattern corresponding topattern P3. Thus, it is ideal carry out the dark correction using thecarriers (dark image information) read before the irradiation in patternP3.

In Embodiment 3, as distinct from Embodiment 1 described hereinbefore,and as in Embodiment 2, the storages times t₁, t₂, t₃ and t₄ for therespective patterns P1-P4 are different from one another, and thecharacteristics of the dark image information are different. It istherefore desirable to have plural pieces of dark image information forthe respective patterns (four patterns P1-P4 in this case).

Embodiment 4

Next, Embodiment 4 of this invention will be described with reference tothe drawings. FIG. 12 is a timing chart of frame rates and signalsrelating thereto according to Embodiment 4. The X-ray apparatus and FPDin Embodiment 4 also have the same constructions as in Embodiments 1-3described above. Thus, their description will be omitted, and only thedifference will be described.

The difference to Embodiment 3 lies in that the controller 10 (see FIG.1), as in Embodiment 2, has an area changing function for changing areaswhere the reading of carriers at the irradiation time is started. It isthe same as in Embodiment 3 that the reading of carriers at theirradiation time is carried out continuously according to all the areasof an image. That is, Embodiment 4 is an implementation mode combiningEmbodiment 2 and Embodiment 3.

Specifically, as shown in FIG. 12, the reading of carriers before theirradiation is carried out in the order of areas D3, D4, D1 and D2, andthe reading of carriers at the irradiation time is carried outcontinuously according to all the areas of the image. This is carriedout continuously in the order of areas D1, D2, D3 and D4. As inEmbodiment 3, the frame rate before the irradiation is T₁ and the framerate after the irradiation is T₂.

With the X-ray apparatus according to Embodiment 4 described above, asin Embodiment 3, the reading of carriers at the irradiation time iscarried out continuously according to all the areas of an image, wherebythe reading is carried out faster than the carrier reading before theirradiation. As in Embodiment 2, the luminance difference occurring atthe boundary between divided images when reading carriers fromintermediate areas can be solved by starting the reading of carriers atthe irradiation time from the first area (D1 in FIG. 12).

In Embodiment 4, as in Embodiment 2 described hereinbefore, the area forstarting the reading of carriers at the irradiation time is changed tothe first area, such that the reading of carriers at the irradiationtime is started from the first area (D1 in FIG. 12). However, as notedabove, the area for starting the reading of carriers at the irradiationtime is not limited to the first area, but may be any arbitrary area.

The case of applying the dark image information to the timing chart ofFIG. 12 as in Embodiment 4 will be described with reference to FIG. 13.FIG. 13 is an explanatory view of the dark image information accordingto Embodiment 4. In carrying out a dark correction, as shown in FIG. 13,the carriers for areas read with the same timing as in FIG. 12 andwithout outputting X-ray pulses are read as carriers at the X-raynon-irradiation time. The dark correction is carried out by using thecarriers read as dark image information. In this case, the reading takesfour patterns P1, P2, P3 and P4 as shown in FIG. 13

Specifically, in pattern P1, carriers are read before the irradiationseparately in the order of areas D1, D2, D3 and D4, and carriers areread at the irradiation time continuously in the order of areas D1, D2,D3 and D4. In pattern P2, carriers are read before the irradiationseparately in the order of areas D2, D3, D4 and D1, and carriers areread at the irradiation time continuously in the order of areas D1, D2,D3 and D4. In pattern P3, carriers are read before the irradiationseparately in the order of areas D3, D4, D1 and D2, and carriers areread at the irradiation time in the order of areas D1, D2, D3 and D4. Inpattern P4, carriers are read before the irradiation separately in theorder of areas D4, D1, D2 and D3, and carriers are read at theirradiation time continuously in the order of areas D1, D2, D3 and D4.

As in Embodiments 1-3, a storage time from start of a previous area,identical to start of an area to be imaged, to start of the area to beimaged is referred to as t₁ for area D1, t₂ for area D2, t₃ for area D3and t₄ for area D4. Storage times t₁, t₂, t₃ and t₄ for the respectiveareas, when expressed in terms of frame rate T and read period t_(READ),are as follows, as shown in FIG. 13.

In pattern P1, t₁−5×T₁, t₂=4×T₁+t_(READ), t₃−3×T₁+2×t_(READ) andt₄=2×T₁+3×t_(READ). In pattern P2, t₁=2×T₁, t₂=5×T₁+t_(READ),t₃=4×T₁+2×t_(READ) and t₄=3×T₁+3×t_(READ). In pattern P3, t₁=3×T₁,t₂=2×T₁+t_(READ), t₃=5×T₁+2×t_(READ) and t₄−4×T₁+3×t_(READ). In patternP4, t₁=4×T₁, t₂=3×T₁+t_(READ), t₃=2×T₁+2×t_(READ) andt₄=5×T₁+3×t_(READ).

As in Embodiments 1-3, the characteristics of dark image informationwill change depending on the length of storage times t₁, t₂, t₃ and t₄.Thus, when, as shown in FIG. 12, images are processed by carrying outthe reading of carriers before the irradiation separately in the orderof areas D3, D4, D1 and D2, and the reading of carries at theirradiation time is carried out continuously in the order of areas D1,D2, D3 and D4, the imaging will be in a pattern corresponding to patternP3. Thus, it is ideal carry out the dark correction using the carriers(dark image information) read before the irradiation in pattern P3.

In Embodiment 4, as distinct from Embodiment 1 described hereinbefore,and as in Embodiments 2 and 3, the storages times t₁, t₂, t₃ and t₄ forthe respective patterns P1-P4 are different from one another, and thecharacteristics of the dark image information are different. It istherefore desirable to have plural pieces of dark image information forthe respective patterns (four patterns P1-P4 in this case).

This invention is not limited to the foregoing embodiments, but may bemodified as follows:

(1) In each of the foregoing embodiments, the X-ray apparatus shown inFIG. 1 has been described by way of example. This invention may beapplied also to an X-ray apparatus mounted on a C-shaped arm, forexample. This invention may be applied also to an X-ray fluoroscopicapparatus and an X-ray CT apparatus.

(2) In each of the foregoing embodiments, the invention is applied to aradiation detector of the “direct conversion type” with the thicksemiconductor film 31 (semiconductor layer) converting incidentradiation directly to charge information. The invention is applicablealso to a radiation detector of the “indirect conversion type” with aconverting layer such as a scintillator converting incident radiationinto light, and a semiconductor layer formed of a light sensitivematerial converting the light to charge information. The light sensitivesemiconductor layer may be formed of photodiodes.

(3) In each of the foregoing embodiments, the X-ray detector fordetecting X rays has been described by way of example. This invention isnot limited to a particular type of radiation detector which may, forexample, be a gamma-ray detector for detecting gamma rays emitted from apatient dosed with radioisotope (RI), such as in an ECT (EmissionComputed Tomography) apparatus. Similarly, this invention is applicableto any imaging apparatus that detects radiation, as exemplified by theECT apparatus noted above.

(4) In each of the foregoing embodiments, the radiation detector fordetecting radiation, typically X rays, has been described by way ofexample. This invention is applicable also to a photodetector fordetecting light. Thus, the invention is not limited to any device thatforms images by detecting light.

(5) Each of the foregoing embodiments is an implementation mode based oncarrier reading which carries out the reading of carriers before theirradiation separately according to the images of divided areas, but maybe an implementation mode based on the storage of carriers instead. Thatis, the storage of carriers may be carried out separately according tothe images of divided areas. Then, the controller 10 (see FIG. 1) willhave a storage and readout stopping function to stop the storage andreading of carriers before the irradiation. The controller 10corresponds to the storage and readout stopping device in thisinvention.

(6) In each of the foregoing embodiments, the setting is made to readcarriers before the irradiation periodically, and interpose, in anarbitrary cycle, a non-reading operation between reading in that cycleand reading in the following cycle. However, it is not absolutelynecessary to synchronize it with the cycles. In this case, thecontroller 10 (see FIG. 1) may have a storage and readout stoppingfunction to stop the storage and reading of carriers before theirradiation, even if the storage and reading of carriers before theirradiation is only halfway through an image, according to the image ofa divided area corresponding to the halfway area, and the X-ray tubecontroller 7 (see FIG. 1) may have a function to control to emit X raysafter the storage and reading of carriers before the irradiation isstopped by the storage and readout stopping function of the controller10. The controller 10 corresponds to the storage and readout stoppingdevice in this invention.

(7) In each of the foregoing embodiments, the dark image informationread at the non-irradiation time for use in the correction consists ofthe carriers read before the irradiation. As shown in FIG. 14, this maybe carriers read after the irradiation. In this case, a dark correctionis carried out using as dark image information the carriers for areas(see the hatched areas in FIG. 14) read after imaging with the sametiming as the imaging and without outputting X-ray pulses.

(8) In each of the foregoing embodiments, the image dividing mode is asshown in FIG. 5, but this is not limitative. As shown in FIG. 15, forexample, it may be divided vertically into two equal parts. This case isuseful particularly to an FPD that reads independently upward ordownward through the data lines 34. The image may be divided laterallyalong the data lines 34.

(9) This invention is applicable to both a method of reading one line ata time through the data lines, and a method of reading by a plurality oflines through the data lines.

(10) In each of the foregoing embodiments, the X-ray irradiation enablesignal is continuously outputted without synchronizing with a firstframe synchronization signal outputted after a shift to preparation forX-ray irradiation, and is stopped synchronously with a framesynchronization signal outputted next, but this is not limitative. Asshown in FIG. 16, the X-ray irradiation enable signal may becontinuously outputted without synchronizing with the next framesynchronization signal, to be stopped synchronously with a framesynchronization signal outputted further next, thereby extending theX-ray irradiation enable time to set the emission of X-ray pulses long.Thus, by increasing the periodic number of the frame synchronizationsignal with which stopping of the X-ray irradiation signal issynchronized, the X-ray irradiation enable time can be extended furtherto set the emission of X-ray pulses to be still longer.

1. An imaging apparatus for obtaining images by carrying out imagingbased on light or radiation, comprising a conversion layer forconverting light or radiation information to charge information inresponse to incident light or radiation, and a storage and readingcircuit for storing and reading the charge information converted by theconversion layer, the apparatus being constructed to obtain the imagesbased on the charge information read by the storage and reading circuit,the apparatus further comprising a first storage and readout settingdevice for dividing an image into a plurality of predetermined areas,and setting storage and reading of the charge information beforeirradiation of the light or radiation according images of the dividedareas.
 2. The imaging apparatus according to claim 1, comprising astorage and readout stopping device for stopping the storage and readingof the charge information before the irradiation, even if the storageand reading of the charge information before the irradiation is onlyhalfway through an image, according to the image of a divided areacorresponding to the halfway area, and an irradiation control device forcontrolling to carry out the irradiation after the storage and readingof the charge information before the irradiation are stopped by thestorage and readout stopping device.
 3. The imaging apparatus accordingto claim 1, comprising a second readout setting device for reading thecharge information before the irradiation periodically, and interposing,in an arbitrary cycle, a non-reading operation between the reading inthat cycle and reading in a following cycle.
 4. The imaging apparatusaccording to claim 3, comprising a readout stopping device for stoppingthe reading of the charge information before the irradiation, even ifthe reading of the charge information before the irradiation is onlyhalfway through an image, according to the image of a divided areacorresponding to the halfway area, and synchronously with a cyclecorresponding to halfway timing, and an irradiation control device forcontrolling to carry out the irradiation after the reading of the chargeinformation before the irradiation is stopped by the readout stoppingdevice, and at a time of the non-reading operation.
 5. The imagingapparatus according to claim 4, wherein the reading of the chargeinformation before the irradiation is carried out periodically in orderof divided adjoining areas, and when a last area is finished, a returnis made to a first area for repetition.
 6. The imaging apparatusaccording to claim 5, wherein the reading of the charge information atan irradiation time is started from a next area adjacent the area wherethe reading of the charge information is stopped, the reading of thecharge information at the irradiation time is carried out periodicallyin the order of the divided adjoining areas from the starting area, andwhen the last area is finished, a return is made to the first area forrepetition.
 7. The imaging apparatus according to claim 5, comprising anarea changing device capable of changing areas where the reading ofcarriers at the irradiation time is started, wherein the reading of thecharge information at the irradiation time is carried out periodicallyin the order of the divided adjoining areas from the starting area, andwhen the last area is finished, a return is made to the first area forrepetition.
 8. The imaging apparatus according to claim 7, wherein thearea changing device is arranged to start the reading of the chargeinformation from the first area.
 9. The imaging apparatus according toclaim 5, wherein the reading of the charge information is carried outcontinuously according to all areas of the image.
 10. The imagingapparatus according to claim 1, comprising a correcting device forcorrecting charge information read at an irradiation time based oncharge information read at a non-irradiation time of the light orradiation.
 11. The imaging apparatus according to claim 10, wherein thecharge information read at the non-irradiation time for use in thecorrection is the charge information read before the irradiation. 12.The imaging apparatus according to claim 10, wherein the chargeinformation read at the non-irradiation time for use in the correctionis charge information read after the irradiation.
 13. The imagingapparatus according to claim 10, wherein the charge information read atthe non-irradiation time for use in the correction consists of more thanone piece.